Touch screens are widely used in various applications, such as automated teller machines, mobile phones, laptops, desktops, etc. A touch screen is used for detecting different types of user inputs. Compared to external input devices e.g., a keyboard, a mouse), a touch screen is often considered as a more effective interface in terms of convenience, flexibility and cost. A touch event on a touch screen may be sensed through various methods, such as, capacitance sensing methods. For example, a user touches a point on a touch button (or a touch pad, a touch screen). The presence or movement of a user's finger in the vicinity of the touch button disturbs or changes the electric field associated with the capacitance of the touch button and thus modifies the capacitance of the touch button. Therefore, the touch event may be detected according to the capacitance change.